The pharmaceutical business is not kind to entrepreneurs. It takes more than a decade and hundreds of millions of dollars in venture capital to get from cool idea to marketed drug, which is why the founders of Amgen, Genentech and Gilead were gone by the time those companies became big successes. But nestled near a pastoral local farm 40 minutes outside of New Haven, Conn., amid ears of corn and rows of beets, is the exception to that rule. There, an unassuming, self-deprecating doctor named Leonard Bell still serves as chief executive of Alexion Pharmaceuticals, the company he founded after he quit his medical professorship at Yale 20 years ago.